THIS invention relates to a method of producing inorganic semiconducting nanoparticles having a stable surface.
Semiconductor nanoparticles, with a characteristic size of a few nanometres up to several hundred nanometres, are a widely studied type of material, in which size effects dominate over properties of the bulk material. Depending on the application, single particles may be dispersed randomly in a matrix (quantum dots, OLEDs. DSC cells, organic semiconducting inks); regularly arranged (photonic arrays); or form an interconnecting structure (inorganic semiconducting inks). The latter may be a close packed structure, random network or a fractal agglomeration of different sized clusters.
In basic scientific studies a stable, well characterised surface is required, which has led to nanotechnology being seen as an expensive, high technology option, with complex synthesis and handling techniques. Bare, undecorated silicon surfaces are only stable under ultra high vacuum conditions. Many nanoparticles produced by wet chemical synthesis, e.g. silicon nanoparticles such as those described by Baldwin et al (Chemical Communications 1822 (2002)) are terminated with long alkyl chains, which act as a surfactant to prevent aggregation and the growth of larger particles.
On bulk silicon surfaces thermal oxides may be tens or even hundreds of microns thick, and depending on temperature and humidity, the native oxide normally grows to a thickness of 5-10 nm. A layer this thick would obviously insulate any nanoparticle and dominate its electrical properties.
In a previous patent application of the present applicants (WO 2007/004014) the described invention exploited the observation that, after the particles have been produced, oxidation is self limiting, at one monolayer or less, and forms a stable surface, so that electrical conduction can occur unhindered between interconnecting particles.
It is an object of the invention to provide an alternative method of producing semiconducting nanoparticles from bulk material.